An optical signal can include of a continuum of wavelengths over a finite spectral band, or alternately, it may comprise a few discrete wavelengths or spectral bands. Such spectral bands may be used in dense wavelength division multiplexing systems for fiber optic telecommunications. When designing certain optical systems for control of optical signals, it is sometimes advantageous to insure that the different wavelengths of light that pass through the system do so in precisely the same amount of time. Such systems are said to have zero dispersion. Optical systems may also be designed with dispersion such that an optical signal transit time is not the same for all wavelengths of light. A system has negative dispersion if longer wavelengths of light require a longer transit time to pass through the system compared to shorter wavelengths. Similarly, an optical system with positive dispersion requires a longer transit time for shorter wavelengths compared to that of longer wavelengths.
The Treacy compressor is a well-known optical system having negative dispersion, and is commonly employed in the design of ultrashort pulsed laser systems. A traditional Treacy compressor is illustrated in FIG. 1 and includes two separate diffraction gratings 110 and 120 and rooftop mirror assembly 130. Additional mirrors can be employed to route the optical signal into and out of the Treacy compressor, or to fold the optical path within the compressor. In order to function properly, the gratings and mirrors of the Treacy compressor must be carefully positioned and aligned. If not aligned properly, the different wavelengths of light that pass through the Treacy compressor system do not arrive at the same physical location upon exiting the system (a defect known as spatial chirp) or the exact dispersion (wavelength-dependent transit time) will not match the design goal.
The dispersion produced by the traditional 2-grating Treacy compressor can also be achieved with a single grating system that utilizes an extra rooftop mirror assembly in the optical path. This layout is known as a single-grating or 1-grating compressor. The 1-grating compressor, while simpler than the traditional 2-grating compressor, still requires meticulous positioning and alignment of the grating and rooftop mirror assemblies for proper function and to avoid the defects mentioned above. Additionally, both the 2-grating and 1-grating embodiments of the Treacy compressor suffer from susceptibility to misalignment over time due to shifts in spatial orientation or position of the various optomechanical elements in relation to one another. Element shifts can be caused by environmental factors such as temperature change, mechanical shock or vibration, shrinkage of epoxies or adhesives used within the system, or simple mechanical creep and stress relaxation of the various parts of the system.
An optical system that produces a desired amount of dispersion while requiring less alignment and being less susceptible to misalignment shift over time would be advantageous.